An important function performed by naval ships and naval aircraft is that of scouting or patrol; that is, searching for the enemy. Search is particularly important in antisubmarine warfare. In order to find the submarine, listening systems called sonar systems have been developed to enable the operators of the sonar equipment to detect the submarine.
Sonar systems utilize sound waves which are propagated through the water. Modern sonar systems: receive sound signals from the water, amplify the signals, and analyze the signal so that the sonar operator will receive information about objects and their movement in the sea. The sonar systems may include a variety of devices of varying degrees of complexity. These devices normally include a hydrophone array that transforms or transducers acoustic energy to electric energy, followed by some form a signal processing to feed an aural or visual display suitable for the human observer.
The sounds produced by man made objects like submarines have a different periodicity than the noise usually found in the ocean. Man made sounds propogate through the water. They have pressure peaks and pressure valleys like a wave or ripples on a pond. The foregoing waves are detected by a plurality of hydrophones that comprise a hydrophone array. One type of hydrophone array utilized in the prior art is disclosed in Woodruff, et al, U.S. Pat. No. 4,004,265, which issued on Jan. 18, 1977. Each hydrophone in the array would receive the peaks and pressure valleys of the sound wave at different times. In order for the hydrophones to produce useful information that would enable one to determine the location of a submarine, the peaks and valleys of the waves must be placed in phase. One method utilized in the prior art for placing the peaks and valleys in phase involved a process called steering. The arrays were mechanically steered by physically rotating the array elements, or the array elements were electrically steered by inserting in series with each array element appropriate phasing networks (for narrowband arrays) or time delay networks (for broadband arrays) that effectively placed the array elements along the path of the sound wave. The sine waves received by the array elements were combined, transmitted on a wire, demultiplexed and transmitted to a beamformer.
For every hydrophone in the hydrophone array there was a multiplexer. The multiplexer multiplexed the signals that were obtained from each hydrophone onto a common conductor and transmitted them to a receiver. In order to obtain individual hydrophone signals, the received signals were demultiplexed and input to a beamformer which contains a computer and a memory having many storage locations for each hydrophone. The computer processed the stored amplitude and phase of the received signals and arranged the signals with respect to their relative arrival time. Then the computer transmitted the signals to a spectrum analyzer and sonar scope where the signals would be observed and analyzed. One of the disadvantages of the foregoing method of producing beams was that a large amount of electronic equipment was needed to manipulate the stored amplitude signals with respect to the relative arrival time of the signals. The electronic equipment was expensive and required a large amount of space.